1. Field of the Invention
This invention relates to flip-chip packages and more particularly relates to overcoming laminate warpage and misalignment in flip-chip packages.
2. Description of the Related Art
Flip-chips, or Controlled Collapse Chip Connection (“C4”) chips, are semiconductor devices that are attached to an external substrate by an array of contacts on the chip. The connections between the contacts on the chip and pads on the external substrate are usually made using solder. Solder, however, has poor electromigration performance. Electromigration in solder joints causes a gradual movement of ions within the solder, which can lead to decreased reliability and eventual loss of the connection and failure of the entire circuit.
Using less solder in the flip-chip interconnects can minimize the effects of electromigration. Decreasing the amount of solder, however, increases alignment issues and substrate warpage issues between the flip-chip and the substrate. When less solder is used, flip-chip misalignment and substrate warpage can cause failed, non-wet connections between the flip-chip and the substrate, as there is not enough solder to compensate for the misalignment or for the variation in contact pad heights on the substrate due to substrate warpage.
To compound the issue, modern high-performance chips have higher connection counts. To accommodate more connections, flip-chips often have decreased pitches, or distances between contacts, or even smaller contacts themselves. This smaller scale amplifies even the smallest chip misalignment or substrate warpage. Additionally, to meet the demands of these high density chips, substrates are becoming thinner, with higher density signal traces and vias. Organic laminates are often used for these flip-chip package substrates. Organic laminate substrates are much more subject to warpage than are ceramic substrates. There is also a larger coefficient of thermal expansion (“CTE”) mismatch between organic laminate substrates and silicon than between ceramic substrates and silicon. Further, the warpage in organic laminates is not consistent, and can vary in shape and severity even between individually diced laminate blocks cut from a single laminate panel.